This invention relates to a solid waste comminuting apparatus. Such devices have been established in the art and are now widely used in a variety of industrial applications, such as municipal waste treatment and industrial applications. Reference is made to U.S. Pat. No. 4,046,324, which discloses such a basic system that has achieved commercial success.
By definition, comminution is the reduction of particle size of solid waste material to minute particles. It is generally performed by shearing, shredding and crushing of the waste material. As set forth in the '324 patent, comminution occurs by utilizing a pair of counter-rotating intermeshed cutting members.
The solid waste material is fed into the interface between cutting elements, typically utilizing a fluid carrier medium, and shearing action occurs because the two cutters overlap each other such that opposing forces of counter-rotation of the cutting elements on the different stacks act on the solid material as it passes through the device.
In practice, such devices are generally used in an enfluent path. That is, the solid material is generally entrained in a liquid and the device is placed directly in the liquid stream. By having the solid material entrained in a liquid stream transportation of the material to and from the unit occurs. Further, by softening the solid particles, a greater degree of comminution is achieved. Devices of the type disclosed in the '324 patent have found commercial success and are widely used in waste treatment facilities, shipboard use and the like. As can be appreciated, the environment of use is very harsh for the equipment and as such, routine maintenance is required in both a preventative sense and also to immediately repair break downs when they occur thus minimizing system down-time.
An important aspect of such maintenance and repair is the integrity of the seals which provide the cutter stacks to rotate while minimizing friction. Given the mass of the cutter stacks together with high motor torque, loads on the seals are large and thus seal integrity is a primary consideration. In the past, two-shafted machines such as the '324 device required that the seal assembly be an integral part of the device. Such is illustrated in FIG. 1 of the '324 patent. As a result, if there was a seal failure other critical components of the device were likely to be effected. This failure of a seal could thus mean that bearings could fail and seize up the cutter stack.
Importantly, to repair the seal assembly, in the prior art, there was a requirement that the device be disassembled and completely reassembled. In the context of a unit which is used in fluid waste treatment that down-time, in some cases as long as a day could have detrimental effects in the ability of a plant to process waste. Such would require rerouting solid waste, shutting down a portion of the facility and otherwise result in an inefficient operation.
Moreover, in prior art two-shafted machines, the cutter stack and the various seal components were integral and in-line with a fixed geometry. Consequently, tightening of the cutter stack, by compression, resulted in compression of the seals. Again, such is illustrated in FIG. 1 of the '324 patent. It has been recognized however, that under normal operating conditions the cutter thickness experiences wear and thus the overall thickness of the stack tends to reduce over time. The result is an effective reduction in the overall stack height and the stack therefore tends to become loose. As a consequence, initial compression of various seal components is lost and the seal faces tend to separate. The result is leakage across the seal with the subsequent result of bearing failure.
Another deficiency in the prior art was the use of a labyrinth between the main fluid chamber and the seal faces. The labyrinth was generally incorporated into the seal components as sacrificial component. Because such devices are used in applications which include a high grit content, the labyrinth tended to be a relatively high wear component. As a consequence, seal components had to be removed to replace the labyrinth with the potential for seal damage upon reassembly.